Buying a Power Support Unit (PSU)?

The motherboard have arrived today but I don't have a Power Supply Unit (PSU) yet. It seems that I did not pay much attention to the PSU and took things for granted. Luckily I didn't make any unnecessary purchase and decided to wait (limited budget) and research more before making any buying that I will regret later. Three things need to take into consideration when buying a PSU. First, power connector type of your motherboard, the required power needed, and lastly, the power efficiency needed.

First, normal and high-end (like server or workstation) motherboard have different power consumption which determines different connector type. There are different type of connector (differentiate by number of pins) which provides additional power to your CPU. Normal desktop uses 4-pin connector where server or workstation uses 8-pin connector. To quote Wikipedia (emphasis added),
ATX12V 4-pin power connector (also called the P4 power connector). A second connector that goes to the motherboard (in addition to the main 24-pin connector) to supply dedicated power for the processor. For high-end motherboards and processors, more power is required, therefore EPS12V has an 8-pin connector.
The screenshot below (credit to Mark Allen) shows different type of power connector used by the motherboard. The 8 pin EPS connector and 4+4 pin connector (not EPS compliance) are equivalent. Unless you can find 4-pin to 8-pin adapter (not sure this is applicable for server motherboard), best to just find the right PSU which support the number of pin needed. 4+4 pin is your best bet.



Next, determine (or through this site as well) the load wattage needed. Fill in the type of machine and all its components needed, you will have an estimation of power required. Unless you're always upgrading your machine, buy the one nearest to your required load wattage. My calculation of my hardware specification yields around 273W needed.

The next question is how many watts should you get? Remember, you will not fully utilize 500W out of the PSU as there is no way for 100% efficiency usage. Energy will be leaked due to heat. For example, a PSU with maximum power (also known as peak power) output of 500W, continuous voltage power (you may look for wording like 'combine +12V' or 'max combined power') of 450W, and rating of 80% efficiency under certain load. Then, the actual energy drawn continuously from the PSU is 360W. That basically fulfill the energy requirement I've calculated earlier.

Lastly, determine the power efficiency. Unless you're running a server for 24/7, goes for anything PSU with 80 Plus standard, 80 Plus Bronze standard should be good enough. You can choose from different manufacturers. However, rating sometimes can be misleading. PSU is as good as its capacitor used and there are many different tier of capacitor manufactures. Tom's hardware provides a good list of matching PSU manufacturers and capacitor manufacturer. Use that list to make an informed purchase. Another way to determine whether the particular PSU is using a good capacitor is check the warranty period. Longer warranty given indicates better components or capacitor used.

My research leads me to these PSUs due to availability and budget. Since this is not an urgent buy, might as well sleep through it and revisit it from time to time.


In conclusion, follow these following steps.

  1. Determine your form factor. Is it ATX, micro-ATX, or something else?
  2. Estimate your load wattage need based on the component needed.
  3. Calculate the actual wattage needed from your PSU.
  4. Check the PSU manufacturer tier list and see which brand and model use the best capacitor.
  5. Select the PSU with 80 Plus Bronze rating that fit your budget.
  6. Google for any reviews of the selected PSU brand and model.
  7. Buy the PSU.

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